(1) Field of the Invention
This invention relates to a warmth keeping vessel made of ceramics or porcelain and a method of producing the same.
(2) Description of the Prior Art
Vessels made of ceramics or porcelain are utilized mostly, for example, as tableware. In order to serve as tableware, it is not sufficient for them to be vessels for merely containing things. That is to say, the vessels are required to keep the temperature of foods within them to elongate the tasting time of the foods, in other words, to be able to keep warm things warm for a fixed time and to keep cold things cold for a fixed time.
Now, ceramic or porcelaneous products are so comparatively low in the warmth keeping effect that a conventional method taken to bring a warmth keeping effect is to increase the thickness of a ceramic or porcelaneous vessel itself, to preheat the vessel with hot water or the like or to keep the vessel cool in advance in a refrigerator or the like. However, it has been still insufficient to elongate the above described tasting time. In order to make it sufficient, it is thought to make a ceramic or porcelaneous vessel of a sealed double-walled structure as in a thermos bottle.
However, the ceramic or porcelaneous product is made by heating and firing kaolin above 1000 degrees. Therefore, even if an airtight hollow chamber is formed of double walls by molding kaolin in a vessel mold, when it is simply baked, air within the hollow chamber will expand due to heating and the warmth keeping ceramic or porcelaneous vessel itself will break. Thus, it has been difficult to seal a hollow chamber with heating and firing.
Therefore, there is a method wherein holes through which a hollow chamber formed of double walls communicates with the atmosphere are made in the double walls and then the vessel is fired.
In this method, air between the double walls will be replaced with the atmospheric air through the holes, heat will be exchanged and therefore the warmth keeping effect will be insufficient. In case such vessel is seen as an article, if the joint to make the double walls remains and the holes made in the double walls are conspicuous, the value as of an article will reduce.